Hollow-tubed systems are used in a variety of applications. For example, Electrical Metallic Tubing (“EMT”) conduit systems include elongate, thin walled, non-threaded tubes that are usually formed of metal. EMT tubes are used to enclose electrical wires therein. Similar systems include Rigid Metal Conduit (“RMC”), Galvanized Rigid Conduit (“GRC”), Intermediate Metal Conduit (“IMC”) and Polyvinyl Chloride (“PVC”) conduit, Armored Cable:AC(BX), Metal Clad Cable:MC and Flexible Metal Cable:FMC. Other materials such as plastic, fiber or fired clay can be used as well.
A typical EMT, RMC, or other conduit system usually includes electrical junction boxes, a plurality of EMT tubes, and other electrical systems that are joined together with fittings to provide a continuous protected chamber for receiving electrical wires and their connections therein. These fittings join the tubes to the junction boxes, and they also are used to join two or more sections of tubes together.
Currently, fittings for joining these elements together have undue limitations. For example, one common fitting includes a connector body with an internally threaded compression nut screwed on to body of a fitting which has external male threads. The end portion of a tube is slidably received within the compression fitting, and a worker must tighten the compression nut to compress a steel gland ring pre-installed between a compression fitting body and compression nut to secure the tube within the fitting. In practice, workers can over-tighten some compression nuts to strip both female and male threads of a compression fitting this usually leave tube not secured or not locked in the position of a compression fitting. Alternatively, the worker can under-tighten the a compression nut to the male threads of a compression fitting, thereby allowing the tube to become disconnected over time and expose the wiring unsecured within the tube.
In some cases, when any exterior threads on a compression fitting body or interior threads on a compression nut are not threaded or machined properly, the exterior threads on the compression fitting body and interior threads on a compression nut will not engage or mate well. This misalignment can cause scraping along the entire compression fitting or a loose connection, thereby allowing the tube to become disconnected over time and expose the wiring unsecured within the tube.
Another common fitting includes a body with a perpendicularly mounted threaded set screw. The end portion of a tube is slidably received within the body of a set screw fitting, and a worker must tighten the set screw to secure the tube within the fitting. In practice, workers can over tighten some set screw placing excessive pressure on a localized portion of the tube. In some cases, this excessive pressure can damage the tube. Over-tightening one or two set screw can strip the female threads in the screw boss. Alternatively, the worker can under-tighten the set screw, thereby allowing the tube to become disconnected over time and expose the wiring secured within the tube.
A typical conduit system can have hundreds of these fittings, all of which require hand tightening of each compression nut and set screw on each fitting. The labor of performing this repetitive task can increase the overall cost of a project.
On the manufacturing side of making millions of pieces of these fittings, all of which require a section of tube cut into a defined length to form each compression nut. After forming a piece of tube into a compression nut, manufacturing workers must tap each nut with internal threads. In addition, each compression nut must be secured to a compression connector or a compression coupling. In addition, each compression connector or coupling body must be also be formed in a similar manner with threads being formed on one end of each connector and two threads being formed on each compression coupling.
Set screw type connectors or couplings require labor to punch holes and tap threads on each screw hole, thereby increasing the cost of production. With millions of set screw fittings, compression fittings including compression nuts currently being manufactured each year and each fitting being large and relatively heavy, the cost of energy used in production and transportation, and other transportation related expenses are high. Moreover, the couplings are usually zinc plated, and their relatively large size necessarily increases the amount of zinc plating used, thereby potentially increasing the adverse effects on the environment.
More recently, efforts have been made to provide a snap-in securing system for joining armored MC, AC (BX) and FMC cables to junction boxes and the like. Examples of these types of systems can be found in U.S. Pat. No. 3,272,539 to R. W. Asbury, Sr.; U.S. Pat. No. 3,858,151 to Paskert; U.S. Pat. No. 6,670,553 to Gretz; and U.S. Pat. No. 6,939,160 to Shemtov, all of the disclosures of which are hereby incorporated by reference.
In general, these fittings include a ferrule with one or more annularly mounted tabs or cantilevered snap clips extending therefrom. The tabs and cantilevered snap clips operably engage a portion of the surface of the armored MC, AC (BX), and FMC cables received therein. While these systems prevent the need for set-screws, they can become loose over time and they provide little alignment guidance to assure that they are properly set when installed.